Why is TCP IP often called a protocol stack rather than a protocol suite?

The protocol stack used on the Internet is the Internet Protocol Suite. It is usually
called TCP/IP after two of its most prominent protocols, but there are other protocols
as well. The TCP/IP model is based on a fi ve-layer model for networking. From
bottom (the link) to top (the user application), these are the physical, data link, network,
transport, and application layers. Not all layers are completely defi ned by the
model, so these layers are "fi lled in" by external standards and protocols. The layers
have names but no numbers, and although sometimes people speak of "Layer 2" or
"Layer 3," these are not TCP/IP terms. Terms like these are actually from the OSI Reference
Model.
The TCP/IP stack is open, which means that there are no "secrets" as to how it
works. (There are "open systems" too, but with TCP/IP, the systems do not have to be
"open" and often are not.) Two compatible end-system applications can communicate
regardless of their underlying architectures, although the connections between layers
are not defi ned.
The term "protocol stack" is often used synonymously with "protocol suite" as an
implementation of a reference model. However, the term "protocol suite" properly
refers to a collection of all the protocols that can make up a layer in the reference
model. The Internet protocol suite is an example of the Internet or TCP/IP reference
model protocols, and a TCP/IP protocol stack implements one or more of
these protocols at each layer.